Composition of polymers derived from renewable resources

ABSTRACT

The present invention relates to a polymer composition comprising polylactide and, based on the weight of this polymer, from 17 to 25 wt % of a chain modifier, from 30 to 55 wt % of an elastomeric polymer and from 20 to 45 wt % of a plasticizer. The invention also relates to the method of preparing said composition as well as to the method of manufacturing an article starting from said composition and the article per se.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of PCT/EP2011/001821, filed Apr. 12,2011, which claims priority from BE 2010/0239, filed Apr. 13, 2010.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a polymer composition obtained fromrenewable resources, in particular polylactide (PLA), as well as toobjects obtained by the usual methods of plastics processing startingfrom this composition.

In particular, the polymer composition of the invention comprises apreferably phthalate-free plasticizer, as well as additives forimproving its impact toughness; more particularly, the present inventionrelates to this type of polymer composition obtained from renewableresources having properties of elongation at break above 200% as well asimproved properties of heat resistance.

The present invention also relates to objects having a set of improvedmechanical and thermal properties, obtained starting from thiscomposition by usual methods of plastics processing, notably bymoulding, by thermoforming or any other processing technique.

TECHNOLOGICAL BACKGROUND

Synthetic polymers based on compounds from the petrochemical industryhad a considerable industrial impact in the middle of the 20th century.Despite the numerous advantages of these materials, two drawbacks stillremain to be solved: use of renewable resources for their production,and recycling of them after use. Taking into account their intrinsicproperties, polymers obtained from renewable resources have thereforebecome an important alternative and there have been many advances bothfrom the standpoint of synthesis and of processing of these materials.They are used, moreover, for a large number of applications such asmoulding, packaging or textiles.

Among the various polymers obtained from renewable resources, polylacticacid or polylactide (PLA) is one of the most commonly used. Taking intoaccount the use of renewable resources, polymers such as PLA havereceived particular attention, notably for partly replacing certainarticles and mouldings in polyvinyl chloride (PVC), which despite theirgood balance of properties have certain shortcomings from the standpointof wettability or heat resistance.

However, these polymers obtained from renewable resources must also beused for moulding or injection moulding, to make objects that must meetcertain criteria from the standpoint of their mechanical and physicalproperties. It therefore appears necessary to develop compositionscomprising these polymers and containing at least one plasticizer andother additives in order to satisfy the required properties, such asflexibility, hardness, wettability, impact toughness or elongation.Moreover, and depending on policies regarding environmental protection,it is desirable for the plasticizer used to be phthalate-free.

It also appears desirable that the polymer composition should containcompounds for improving impact toughness. In this context, it was oftenfound that the use of phthalate-free plasticizer altered the glasstransition temperature (Tg) of the composition, which consequentlyaffected the impact toughness.

Generally, it goes without saying that we wish to have a favourableeffect on the environment and therefore that the aim is to replace PVCobjects with objects manufactured from polymers obtained from renewableresources.

Moreover, it has become apparent that even compositions based on PVChave certain drawbacks such as insufficient elongation at break, orinadequate heat resistance or wettability, these last two propertiesbeing manifested, for the resultant objects, by the development ofcracks or difficulty in being painted.

Moreover, at present, for certain mouldings, for example figurines, thepolymer compositions from which they are produced should meet at leastthree criteria, namely significantly improved properties of elongationat break, because they must be able to withstand deformation withoutdamage, which can be achieved if the elongation at break is above 200%,a Shore hardness A between 60 and 95 because they must remain stable,and wettability expressed by a surface tension above 34 dyn/cm so thatthey can easily be painted. Now, at present, the existing polymercompositions from which moulded objects or injection mouldings areproduced do not provide all of these properties.

Moreover, it is highly desirable that polymer compositions intended forpreparation of moulded objects, for example figurines, in additionshould have a good balance of other mechanical and physical properties,namely as indicated below:

-   -   Shore hardness D<50;    -   heat resistance expressed by the storage modulus at 54° C.>20        MPa;    -   good impact toughness expressed by a ductility index >30%;    -   total fracture energy >8 Joule;    -   deflection >18 mm and    -   good temperature resistance without crazing.

There is therefore a need to develop polymer compositions obtained fromrenewable resources meeting all these criteria simultaneously andallowing objects to be manufactured by the usual techniques of plasticsprocessing.

SUMMARY OF THE INVENTION

The present invention provides a composition that meets the requiredcriteria of elongation, Shore hardness A and wettability that aredesired while maintaining a good balance of other mechanical andphysical properties as defined above and which makes it possible toobtain objects, by usual methods of plastics processing, that have therequired mechanical and physical properties; said composition comprisingpolylactide, a chain modifier, an elastomeric compound for improvingductility and a plasticizer, which is preferably phthalate-free.

The applicant found that the compositions of the invention not only haveimproved main properties such as minimum elongation at break, level ofShore hardness A and wettability, expressed as surface tension, but alsoall the other desirable mechanical and physical properties.

One aim of the invention is to provide a polymer composition obtainedfrom renewable resources that has, simultaneously:

-   -   a property of elongation at break >200% measured by ASTM method        D-638,    -   Shore hardness A between 60 and 95 measured by ASTM method        D-2240 and    -   wettability, expressed as surface tension >34 dyn/cm measured by        ASTM method D-2578.

Another aim of the invention is that the composition should haveproperties of heat resistance, expressed as storage modulus at 54° C.>20MPa measured by ASTM method D-4062.

Another aim of the invention is that the composition should havemechanical strength expressed as Shore hardness D<50 measured by ASTMD-2240.

Another aim of the invention is that the composition should have aductility index >30% measured by ASTM D-3763.

Another aim of the invention is that the composition should have a totalfracture index above 8 Joule measured by ASTM D-3763.

Another object of the invention is that the compositions should havedeflection above 18 mm measured by ASTM D-3763.

Another aim of the present invention is to provide articles having agood balance of starting properties of said composition by the usualmethods of plastics processing such as thermoforming, extrusion,injection or compression moulding.

Another aim of the present invention is to provide a composition thatgives very little detachment of material during removal from the mould.

The applicant found, unexpectedly, that the composition of the inventionis able to provide a balance of good properties of ductility, hardnessand elongation at break (>200%), as well as good surface properties(smoothness) and mould release properties.

Furthermore, the applicant also found, unexpectedly, that saidcomposition displays good properties of wettability, thus allowingobjects obtained with this composition to be painted easily.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a polymer composition for making mouldedobjects or injection mouldings comprising polylactide and, based on theweight of said polymer, from 17 to 25 wt % of a chain modifier, from 30to 55 wt % of an elastomeric polymer and from 20 to 45 wt % of aplasticizer, which is preferably phthalate-free.

The composition of the present invention therefore comprises polylactideand a set of additives necessarily comprising a plasticizer, achain-modifying additive and an elastomeric polymer of renewable origin,as additive for improving ductility.

The present invention relates to a polymer composition comprising:

-   -   a) polylactide, and based on the weight of this polymer,    -   b) from 17 to 25 wt % of a chain modifier selected from        copolymers and terpolymers comprising ethylene or styrene and an        unsaturated monomer bearing at least one epoxide or carboxylic        acid or carboxylic acid anhydride fraction and optionally a        (meth)acrylate fraction,    -   c) from 30 to 55 wt % of an elastomeric polymer selected from        biodegradable polyesters, aliphatic copolyesters, aromatic        copolyesters and mixtures thereof and    -   d) from 20 to 45 wt % of a plasticizer.

The polylactide used in the composition of the invention has anumber-average molecular weight, expressed in polystyrene (PS)equivalent, generally between 50 000 and 250 000.

In the present invention, polylactide means poly-L-lactide (PL-LA),poly-D-lactide (PD-LA), copolymers based on lactides as well asstereocomplexes of PLA such as those described in patent applicationsWO2008/037773 and WO2008/037772. Preferably, the polylactide ispoly-L-lactide.

The PLA can be used in conjunction with usual stabilizers in order toavoid degradations of coloration or even transesterification.

The applicant found, unexpectedly, that by adding a plasticizer,preferably phthalate-free, and a chain modifier to the elastomericpolymer for improving the ductility, a composition having the requiredproperties was obtained.

In the present invention, chain modifier means all copolymers orterpolymers as described below that will be grafted onto the PLA chain.

The chain modifier is generally selected from copolymers and terpolymerscomprising ethylene or styrene and an unsaturated monomer bearing atleast one epoxide or carboxylic acid or carboxylic acid anhydridefraction and optionally a (meth)acrylate fraction. In the presentinvention, the term fraction is a synonym of group.

Preferably, the chain modifier is selected from copolymers andterpolymers comprising ethylene or styrene and an unsaturated monomerbearing a carboxylic acid anhydride fraction or bearing an epoxidefraction and a (meth)acrylate fraction.

More preferably, the chain modifier is selected from copolymers ofethylene or of styrene and glycidyl (meth)acrylate or maleic anhydrideand terpolymers of ethylene or of styrene, of alkyl (meth)acrylate andof glycidyl (meth)acrylate or of maleic anhydride. Among the alkyl(meth)acrylates, we may mention those whose alkyls have between 1 and 10carbon atoms, for example methyl methacrylate, methyl acrylate, ethylmethacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,2-ethylhexyl acrylate, n-octyl acrylate.

The copolymers of ethylene or of styrene and of glycidyl (meth)acrylateor of maleic anhydride can contain from 50 to 99 wt % of ethylene or ofstyrene and from 1 to 50 wt % of glycidyl (meth)acrylate or of maleicanhydride, preferably from 90 to 98 wt % of ethylene or of styrene andfrom 2 to 10 wt % of glycidyl (meth)acrylate or of maleic anhydride, thetotal of the percentages making 100%.

The terpolymers of ethylene or of styrene, of alkyl (meth)acrylate andof glycidyl (meth)acrylate or of maleic anhydride can contain from 50 to97 wt % of ethylene or of styrene, from 1 to 50 wt % of alkyl(meth)acrylate and from 0.2 to 10 wt % of glycidyl (meth)acrylate or ofmaleic anhydride, the total of the percentages making 100%. Preferablythe terpolymers contain from 55 to 95 wt % of ethylene or of styrene,from 2 to 35 wt % of alkyl (meth)acrylate and from 0.3 to 8 wt % ofglycidyl (meth)acrylate or of maleic anhydride.

Even more preferably, the chain modifier is selected from the copolymersof ethylene and of glycidyl methacrylate and the terpolymers of ethyleneor of styrene, of alkyl acrylate and of glycidyl (meth)acrylate or ofmaleic anhydride.

Among the latter, it is possible to use the copolymer of ethylene and ofglycidyl methacrylate sold under the name Lotader®AX 8840 by ArkemaFrance, the terpolymer of ethylene, of ethyl acrylate and of maleicanhydride sold under the name Lotader®4700 by Arkema France as well asthe terpolymer of styrene, of alkyl acrylate and of glycidylmethacrylate sold under the name Joncryl® by the company BASF.

The terpolymers of ethylene or of styrene, of alkyl acrylate and ofglycidyl methacrylate are truly preferred. In particular it ispreferable to use a terpolymer of ethylene, of methyl acrylate and ofglycidyl methacrylate. An example of such a terpolymer is Lotader®AX8900sold by Arkema France comprising 68 wt % of ethylene, 24 wt % of methylacrylate and 8 wt % of glycidyl methacrylate. The chain modifier isgenerally used in amounts between 17 and 25 wt % based on the weight ofthe polylactide.

A polymer of the elastomeric type, of renewable origin and/orbiodegradable, is used as the compound for improving ductility. In thepresent invention, elastomeric polymer means a polymer having elasticproperties which withstands large deformations while returning to itsoriginal state when the stress is removed. The term renewable applies toa natural resource, the stock of which can be restored in a short periodon the human scale. The term biodegradable applies to an organicmaterial if it is degraded under the action of microorganisms in thepresence of oxygen to carbon dioxide, water and mineral salts and,optionally, to by-products (residues, fresh biomass) or if it isdegraded in the absence of oxygen to carbon dioxide, methane, mineralsalts and creation of fresh biomass.

The polymers of the elastomeric type used in the present invention canbe selected from biopolyesters (biodegradable polyesters). Asbiopolyesters, we may mention polyhydroxyalkanoates, preferablycopolymers of polyhydroxyalkanoates, for examplepoly(hydroxybutyrate-co-3-hydroxyvalerate) (PHBV),poly(hydroxybutyrate-co-3-hydroxyhexanoate) orpoly(hydroxyoctanoate-co-3-hydroxydecanoate). The polymers of theelastomeric type used in the present invention can also be selected fromaliphatic or aromatic copolyesters and mixtures thereof such aspoly(butylene adipate-co-terephthalate) and poly(butylenesuccinate-co-adipate). As commercially available products correspondingto this definition that can be used in the composition of the invention,we may mention Ecoflex®, a product sold by BASF or NP EL 01(experimental grade), supplied by NaturePlast, or Apinat® sold by thecompany Api. It is generally used in amounts between 20 and 55 wt %based on the weight of the PLA.

As plasticizer, preferably a phthalate-free plasticizer is used in theinterests of environmental protection, it being understood that otherplasticizers may also be suitable.

Plasticizer means an organic chemical which, when added to thecomposition of the invention, increases the flexibility of the latterand therefore its capacity for being moulded. As phthalate-freeplasticizer that can be used, reference may be made to those mentionedin “Van Nostrand's Encyclopedia of Chemistry”, Fifth Edition, edited byGlenn D. Considine, page 1316. Among these, we may mention for examplephosphates such as tricresyl phosphate, esters of aliphatic dibasicacids such as adipates, sebacates and azelates, esters of fatty acids.Among the phthalate-free plasticizers, we may notably use those from thefamily of citrates, in particular citrate esters (esters of citric acid)such as tert-butylene citrate or tributyl citrate (TBC, CAS number:77-94-1) or butyrate esters (esters of butyric acid) such as triethyleneglycol di-2-ethyl hexyl butyrate supplied by Proviron under the nameL807 (experimental grade) or mixtures thereof. Preferably, TBC is used.The plasticizer is generally used in amounts between 20 and 45 wt %based on the weight of the PLA.

The applicant found, unexpectedly, that by using a compositioncontaining PLA and a mixture of Ecoflex® as agent for improvingductility, Lotader®AX8900 as chain modifier and TBC as plasticizer,using the amounts by weight of the various constituents based on theamount by weight of the polymer obtained from renewable resources (PLA),there was not only improvement of the properties of elongation at break,which was generally >200% with a Shore hardness A between 60 and 95 anda wettability expressed as a surface tension above 34 dyn/cm, but alsoof the properties of mould release, during which detachment of materialwas no longer observed.

The composition of the invention can also comprise additives forimproving the surface finish of the mouldings. Finally the compositioncan also comprise fillers such as talc or other similar fillers withoutaffecting the final properties of the moulded article or injectionmoulding.

The composition of the invention is particularly suitable for mouldingby extrusion, injection or compression or by thermoforming, by usualmoulding processes and with usual operating conditions of temperatureand pressure.

The applicant found, unexpectedly, that if the composition notablycomprised the plasticizer selected from tert-butylene citrate (tributylcitrate) and triethylene glycol di-2-ethylhexyl butyrate, the mouldingscould be removed from the mould easily without any detachment ofmaterial.

The present invention also relates to a method of manufacturing thecomposition according to the invention, characterized in that thepolylactide, the chain modifier, the elastomeric polymer and theplasticizer are mixed in the molten state.

The composition of the invention is generally obtained by mixing thevarious compounds included in the composition. It is generally carriedout at a temperature between 160 and 190° C. Mixing can be carried outin a usual mixer, which can also be a static mixer or in an extruder.When mixing takes place in a mixer, all the compounds can be introducedsimultaneously. If mixing is carried out in an extruder, the plasticizeris preferably introduced after the other compounds, when the latter arealready in the molten state. After mixing, the composition according tothe invention is preferably packaged in the form of granules.

The composition is then intended to be shaped by means of the usualplastics processing techniques, notably by moulding, by thermoforming orany other processing technique for producing articles. The presentinvention thus provides a method of manufacturing an article,characterized in that it consists of transforming the composition of theinvention by moulding by extrusion, by injection, or by compression orby thermoforming.

The invention also relates to an article obtainable by the method of theinvention. Among the latter, we may mention figurines.

EXAMPLES

In the examples according to the invention and the comparative examples,polylactide was used as rigid polymer obtained from renewable resources.More particularly, the poly-L-lactide identified below as PLA 4042 soldby NatureWorks having a number-average molecular weight of about 120 000(PS equivalent) or the poly-L-lactide identified below as PLA 6201 soldby NatureWorks having a number-average molecular weight of about 100 000(PS equivalent) was used.

As chain modifier, Lotader®AX8900 sold by the company Arkema France wasused. Lotader®AX8900 comprises 68 wt % of ethylene, 24 wt % of methylacrylate and 8 wt % of glycidyl methacrylate.

As elastomeric polymer for improving ductility, the poly(butyleneadipate-co-terephthalate) sold by the company BASF under the nameEcoflex® F blend A1200 or NP EL 01 sold in Europe by the companyNaturePlast was used.

As phthalate-free plasticizer, the triethylene glycol di-2-ethylhexylbutyrate supplied by Proviron under the name L807 (experimental grade)or the tributyl citrate (TBC) sold by Jungbunzlauer Landenburg GmbHunder the trade name Citrofol® was used.

The results of the measurements for the examples according to theinvention and for the comparative examples are given below in thevarious tables. The ASTM standards used for measuring the variousproperties are as follows:

-   -   Shore hardness A and D: D-2240;    -   Surface tension: D-2578;    -   Tensile property (elongation at break): D-638;    -   Storage modulus at 54° C.: D-4065;    -   Impact test (ductility, total fracture energy and deflection):        D-3763. The ductility index is expressed on the basis of the        following formula        ((Energy at rupture−Maximum energy)/Energy at rupture)×100.

Examples 1-2

PLA, either 4042 (example 1) or 6201, was placed in an internal mixer ofthe Brabender type, at a temperature of 190° C., at a speed of 40revolutions per minute, for 15 minutes. First a mixture of PLAstabilizers was added (Ultranox 626 and Irganox 1024), and then an agentfor improving ductility as well as a phthalate-free plasticizer wereadded, in the proportions shown in Table 1. TiO₂ was also added to themixer as pigment and chain modifier (Lotader®AX8900).

A composition suitable for injection moulding was recovered from themixer. This composition was injected into a mould for test specimens ata temperature of 190° C. and a pressure of 2 bar. This composition washeld in the mould for 10 seconds. The test specimens were removed fromthe mould and the properties of the moulding were measured.

For all the articles moulded with the composition of the invention, nodetachment of material during removal from the mould was observed.

For all the articles moulded with the composition of the invention,appearance of cracks was not observed, even after thermal treatment inthe range from 20 to 160° C. for 45 minutes (heating at 3° C. perminute).

Example 1

The agent for improving ductility is Ecoflex® F blend A1200.

The plasticizer is L807.

Example 2

The agent for improving ductility is NP EL 01.

The plasticizer is TBC.

It is found that with these compositions, all of the principal desirableproperties are obtained.

TABLE 1 Examples 1 2 References TC2 TC6 Composition (wt %) PLA 46 51Agent improving ductility 23 18 Talc Plasticizer 20 20 Chain modifier 1010 TiO₂ 0.5 0.5 Ultranox 626 0.25 0.25 MID 1024 0.25 0.25 Total 100 100Properties Hardness Izod bars (4 mm) 85 83 Shore A Hardness Izod bars (4mm) 49 40 Shore D Surface Surface tension (dyn/cm) 36 36 Tensileproperties Elongation at break (%) 283 290 Thermo-mechanical Storagemodulus at 54° C. 73.4 42.5 analysis (MPa) Impact test Ductility index(%) 46 33 Total energy (J) 10.2 9.6 Deflection (mm) 19 19

Examples 3 and 4

A composition with PLA that contains all the elements of the formulationallowing the main properties as well as the desirable properties to beachieved was prepared in a twin-screw mixer at a material temperature of180° C.

The PLA is 4042.

The plasticizer is TBC.

The chain modifier is Lotader®AX8900.

Example 3

The agent for improving ductility is NP EL 01.

Example 4

The agent for improving ductility is a mixture of NP EL 01 and Ecoflex®F blend A1200.

Talc was added as an additional constituent in this example.

The results obtained are shown in Table 2.

It can be seen that with these compositions, all of the main anddesirable properties are achieved.

TABLE 2 Examples 3 4 References TC13 TC17 Composition (wt %) PLA 50 53.2Agent for improving ductility NL EL 01 20 10 Ecoflex 6.9 Talc 6.9Plasticizer 19 12 Chain modifier 10 10 TiO₂ 0.5 0.5 Ultranox 626 0.250.25 MD 1024 0.25 0.25 Total 100 100 Properties Hardness Izod bars (4mm) 93 94 Shore A Hardness Izod bars (4 mm) 36 40 Shore D SurfaceSurface tension (dyn/cm) 35 35 Tensile properties Elongation at break(%) 203 207 Thermo-mechanical Storage modulus at 54° C. 39 38 analysis(MPa) Impact test Ductility index (%) 32 33 Total energy (J) 9 12.3Deflection (mm) 20 19

Example 5 (Comparative)

A composition with PLA but not containing an agent for improvingductility was prepared as in examples 1 and 2.

The PLA is 6021.

The plasticizer is L807.

The chain modifier is Lotader®AX8900.

Example 6 (Comparative)

A composition with PLA but not containing an agent for improvingductility was prepared as in examples 1 and 2.

The PLA is 6021.

The plasticizer is TBC.

The chain modifier is Lotader®AX8900.

Example 7 (Comparative)

A composition with PLA but not containing a plasticizer was prepared ina twin-screw mixer at a material temperature of 180° C.

The PLA is 6021.

The agent for improving ductility is NP EL 01.

The chain modifier is Lotader®AX8900.

Example 8 (Comparative)

A composition with PLA but not containing a chain modifier was preparedin a twin-screw mixer at a material temperature of 180° C.

The PLA is 6021.

The agent for improving ductility is NP EL 01.

The plasticizer is TBC.

Example 9 (Comparative)

A composition with PLA that did not contain an agent for improvingductility was prepared in a twin-screw mixer at a material temperatureof 180° C.

The PLA is 6021.

The plasticizer is TBC.

The chain modifier is Lotader®AX8900.

The results obtained for comparative examples 5 to 9 are presented inTable 3. For all the mouldings in comparative examples 5 to 9,appearance of cracks was not observed even after thermal treatment inthe range from 20 to 160° C. in 45 minutes (heating at 3° C. perminute). It can be seen that none of the mouldings satisfies all themain, desirable properties.

TABLE 3 Comparative examples 5 6 7 8 9 References TC1 TC5 TC10 TC11 TC12Composition (wt %) PLA 69 69 69 59 69 Agent for improving 20 20ductility Plasticizer 20 20 20 20 Chain modifier 10 10 10 10 TiO₂ 0.50.5 0.5 0.5 0.5 Ultranox 626 0.25 0.25 0.25 0.25 0.25 MD 1024 0.25 0.250.25 0.25 0.25 Total 100 100 100 100 100 Properties Hardness Izod bars(4 mm) >95 >95 99 92 94 Shore A Hardness Izod bars (4 mm) 62 54 74 39 45Shore D Surface Surface tension 36 36 38 32 35 (dyn/cm) Tensileproperties Elongation at break 253 250 253 258 190 (%) Thermo- Storagemodulus at 28.5 16.7 485 24 6.9 mechanical 54° C. (MPa) analysis Impacttest Ductility index (%) 47 21 27 33 14 Total energy (J) 16 13.5 8.517.2 18 Deflection (mm) 20 19 16 22 22

Examples 10 and 11 (Comparative)

For comparison, the same test specimens were moulded in the sameoperating conditions but with two usual grades of PVC that are generallysuitable for this type of injection moulding.

The results obtained are shown in Table 4.

For all the articles moulded from two grades of PVC, appearance ofcracks was observed after thermal treatment in the range from 20 to 160°C. in 45 minutes (heating at 3° C. per minute).

It can be seen that the elongation at break is barely half what isobtained with the compositions of the invention.

TABLE 4 Comparative examples 10 11 References PVC 88 PVC 92 PropertiesShore Izod bars (4 mm) 86 91 hardness A Shore Izod bars (4 mm) 40 48hardness D Surface Surface tension 32 32 (dyn/cm) Tensile Elongation atbreak (%) 130 125 properties TMA Storage modulus at 20.8 49.3 54° C.(MPa) Impact test Ductility index (%) 25 26 Total energy (J) 9.2 9.3Deflection (mm) 17 18

What is claimed is:
 1. A polymer composition comprising: a) polylactide, and based on the weight of this polymer, b) from 17 to 25 wt % of a chain modifier selected from copolymers and terpolymers comprising ethylene or styrene and an unsaturated monomer bearing at least one epoxide or carboxylic acid or carboxylic acid anhydride fraction and optionally a (meth)acrylate fraction, c) from 30 to 55 wt % of an elastomeric polymer selected from biodegradable polyesters, aliphatic copolyesters, aromatic copolyesters and mixtures thereof and d) from 20 to 45 wt % of a plasticizer.
 2. The polymer composition according to claim 1, characterized in that the polylactide has a number-average molecular weight between 50,000 and 250,000.
 3. The polymer composition according to claim 1, characterized in that the chain modifier is selected from copolymers and terpolymers comprising ethylene or styrene and an unsaturated monomer bearing a carboxylic acid anhydride fraction or bearing an epoxide fraction and a (meth)acrylate fraction.
 4. The polymer composition according to claim 3, characterized in that the chain modifier is selected from copolymers of ethylene or of styrene and of glycidyl (meth)acrylate or maleic anhydride and terpolymers of ethylene or of styrene, of alkyl (meth)acrylate and of glycidyl (meth)acrylate or of maleic anhydride.
 5. The polymer composition according to claim 4, characterized in that the chain modifier is selected from the copolymer of ethylene and of glycidyl methacrylate and the terpolymers of ethylene or of styrene, of alkyl acrylate and of glycidyl (meth)acrylate or of maleic anhydride.
 6. The polymer composition according to claim 5, characterized in that the chain modifier is selected from the copolymer of ethylene and of glycidyl methacrylate and the terpolymers of ethylene or of styrene, of alkyl acrylate and of glycidyl methacrylate.
 7. The polymer composition according to claim 6, characterized in that the elastomeric polymer is selected from poly(butylene adipate-co-terephthalate) and poly(butylene succinate-co-adipate).
 8. The polymer composition according to claim 7, characterized in that the plasticizer is selected from the citrate esters, the butyrate esters and mixtures thereof.
 9. A method of preparing a composition according to claim 8, characterized in that the polylactide, the chain modifier, the elastomeric polymer and the plasticizer are mixed in the molten state.
 10. A method of manufacturing an article, characterized in that it consists of transforming the composition according to claim 8 by moulding by extrusion, by injection, or by compression or by thermoforming.
 11. An article obtainable by the method according to claim
 10. 12. The article according to claim 11, characterized in that the article is a figurine. 